Vulnerability Report: GO-2026-6610

• CVE-2026-78660
• Affects: net/http, net/http/internal/http2, and 1 more
• Published: Oct 08, 2026

Historically, we have been rather lax about malformed framing-related headers in our HTTP/2 implementation, as they cannot interfere with HTTP/2 framing. However, this makes it possible for our HTTP/2 implementation to forward responses containing such headers to an HTTP/1 client when acting as a reverse proxy. If the HTTP/1 client also does not behave strictly enough, this can result in response smuggling.